Method of fabricating a three-terminal voltage surge arrester

ABSTRACT

A method of fabricating a three-terminal voltage surge arrestor comprising the steps of forming an electrically conductive hollow housing having a cylindrical side wall extending between opposed open ends of the housing, the side wall including a longitudinally extending welding flange at each end; disposing a pair of electrically insulative hollow cylindrical members for disposition within the housing adjacent opposing ends thereof; disposing a pair of electrode rods through the ends of said housing, including a means thereon for engaging its associated welding flange as the rod is inserted into the housing through an end thereof to concentricize the rod in the housing; securing one electrode rod to an end of the housing by welding to said welding flange; withdrawing air from the interior of the housing through the other end of the housing; injecting a noble gas into the interior of the housing through said other end of the housing; securing the other electrode rod to said other end of the housing by welding; and isolating a segment of the housing side wall from both electrode rods.

J onassen METHOD OF FABRICATING A THREE-TERMINAL VOLTAGE SURGE ARRESTER[75] Inventor: Gaylord D. Jonassen, Smithtown,

[73] Assignee: Telecommunications Industries, Inc.,

Copaigue, NY.

[22] Filed: Oct. 13, 1972 [21] Appl. No.: 297,412

[52] US. Cl 316/20, 29/25.l6, 317/62 [51] Int. Cl. H01j 9/38 [58] Fieldof Search 29/25.13, 25.16; 317/9 R, 62, 316/17, 18, 19, 2O

[56] 7 References Cited UNITED STATES PATENTS 3,710,191 l/l973 Peche17/62 [4 1 Feb. 12, 1974 57 ABSTRACT engaging its s atedyyqfiiesfheeeestk r a serted into the housing through an ehdlhekedf'iddmcentricize the rod in the housing; securing one electrode rod to an endof the housing by welding to said welding flange; withdrawing air fromthe interior of the housing through the other end of the housing;injecting a noble gas into the interior of the housing through saidother end of the housing; securing the other electrode rod to said otherend of the housing by welding; and isolating a segment of the housingside wall from both electrode rods.

4 Claims, 8 Drawing Figures METHOD OF FABRICATING A THREE-TERMINALVOLTAGE SURGE ARRESTER BACKGROUND OF THE INVENTION 1. Field of theInvention This invention relates to voltage surge arrestors and, moreparticularly, to a method for fabricating a threeterminal voltage surgearrestor.-

2. Description or the Prior Art Three-terminal surge arrestors are wellknown in the art as exemplified by U.S. Pat. No. 3,333,153 issued onJuly 25, 1967 to Wanaselja.

A three-terminal voltage surge arrestor is an ionization chamber formedin an electrically conductive housing wherein a pair of opposedelectrodes are inserted into the chamber with a gap defined between theopposing ends of the electrodes and another gap defined between the endof each electrode and the housing side wall. The two electrodesconstitute the two ac tive terminals of the surge arrestor which areconnected across an electrical instrument to be protected,

whereas the third terminal of the arrestor is defined by the housingside wall which is grounded.

In manufacturing three-terminal voltage surge arrestors, it is importantthat the pair of electrodes is positioned concentrically within theionization chamber and in axial alignment with one another. Also, it isimportant to maintain a desired interelectrode gap between the opposinginner ends of the electrodes. In a true three-terminal voltage surgearrestor, such interelectrode gap should equal the gap between eachelectrode and the housing side wall. It will be realized that thedimensions of these gaps necessarily determine the break downcharacteristics of the voltage surge arrestor, i.e. the maximum voltagepotential across the electrodes prior to ionization of the gas. Inaddition a convenient method of withdrawing air from the ionizationchamber and substituting a readily ionizable gas will substantiallyfacilitate the manufacture of the device.

SUMMARY OF THE INVENTION The method of thisinvention comprises the stepsof forming an electrically conductive hollow housing having acylindrical side wall extending between opposed open ends thereof, theside wall including a longitudinally extending welding flange at eachend; placing a pair of electrically insulative hollow cylindricalmembers within the housing adjacent opposing ends thereof and in spacedapart relation to one another to leave interiorally exposed a centralpart of said conductive housing; placing a pair of rod like electrodesinto said ends of said housing, each electrode including means thereonfor engaging its adjacent welding flange as the electrode is insertedinto the housing to concentricize the rod in the housing; theconfronting ends of said electrodes being spaced from one another adistance substantially equal to the distance said ends are from saidexposed central part of said housing; welding one electrode rod to anend of the housing to seal it thereto; withdrawing air from the interiorof the housing through the other end of the housing; injecting a noblegas into the interior of the housing through said other end of thehousing; welding the other electrode rod to said other end of thehousing to seal it thereto; and isolating a segment of the housing sidewall from both electrode rods.

In a preferred embodiment of this invention, the concentricizing meanson each electrode rod comprises a stop having a base portion of greaterouter diameter that the inner diameter'of the housing, and an inwardlytapered shoulder. If any part of the welding flange on an end of thehousing engages the shoulder as the electrode rod is inserted into thehousing through such end, further inward movement of the rod will causethe rod to shift laterally into concentricity with the housing, whichconcentricity is obtained when the base portion engages the weldingflange. At this point, the rod is restrained from further inward orlateral movement thereby being maintained in concentricity with thehousing.

These and other aspects'and advantages of the present'invention will bemore clearly described with reference to the accompanying drawing.

I BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a longitudinalcross-sectional view of a housing formed in accordance with the methodof this invention;

FIG. 2 is a longitudinal cross-sectional view of an insulative member--formed in accordance with the method of this invention;

FIG. 3 is a side elevation view of a solder ring adapted to be snappedinto an annular groove in the hollow member of FIG. 2;

FIG. 4 is a side elevational view of an electrode formed in accordancewith the method of this invention;

FIG. 5 is a fragmentary cross-sectional view, partly in elevation, of avoltage surge arrestor of this invention shown in one stage of assembly;

FIG. 6 is a cross-sectional view, partly in elevation, of the arrestorof FIG. 5 shown in another stage of assembly;

FIG. 6A is a fragmentary view, similar to F IG. 6 but in enlarged scale,showing one end of said arrestor; and

FIG. 7 is a cross-sectional view, partly in elevation, of thevoltagesurge arrestor of FIG. 6 shown in completed form.

DESCRIPTION OF THE PREFERRED EMBODIMENT The device to be manufactured bythe present method is shown in FIG. 7, wherein it is generallydesignated by the reference numeral 50. The device or surge arrestor 50comprises a pair of insulative tubes 22 which are in axially aligned andspaced apart relation.

Bridging the space between the tubes 22 is a conductive metal segment 42which is in telescoping relation with each tube 22 and its connected inhermetically sealed relation with the telescoping portions of the tube22 by means of solder rings 30. The insulative tubes 22 and theconductive central portion 42 define an outer housing which is capped ateach end by an electrode assembly including an elongated electrodeelement 32 having a cap at its outer end, the cap being formed offlanges 36 and inwardly extending tubular metallic portions 52 welded tosaid flanges, the metallic portions 52 being joined in hermeticallysealed relation to the tubes 3 tween said electrodes and the concentriccenter portion 42.

The interior space defined by the above described structure is filledwith a readily ionizable gas such as a noble gas. As is well known,whenever there is a voltage surge on either electrode (and hence on theline to which it is connected) which is sufficient to cause conductionacross the gap 41 from one electrode 32 to ground as represented by themetal segment 42 the gas will become ionized and will accordinglyestablish conductive paths between the two electrodes 32 and betweenboth electrodes and ground whereby to protect equipment from the voltagesurge.

The method of forming the three-terminal voltage surge arrestor 50 abovedescribed will now be set forth in detail. Referring now to FIG. 1 ofthe drawing, a first step of the method of this invention comprisesforming an electrically conductive hollow housing 10 having acylindrical side wall 12 extending between opposed open ends 14 and 16of the housing. Housing 10 is preferably metallic and most preferablymade of a brazable, weldable metal such as nickel-iron alloy, brass orcooper. Sidewall 12 is preferably circularly cylindrical and preferablyincludes an annular boss 18 formed on the inner surface 19 of the sidewall boss 18 lying substantially intermediate ends 14 and 16. Boss 18 isdefined by a pair of shoulders 19a and 196.

Housing 10 is formed with an outwardly longitudinally extending weldingflange 20 at each end thereof. Preferably, each welding flange isannular and is tapered to a knife edge 23' (see FIG. Alternatively, andif desired, each welding flange 20 may be defined by a plurality ofspaced welding protuberances (not shown) extending outwardly from eachend of the housing and each terminating in a knife edge.

Referring now to FIG. 2, the next step of the method of this inventionincludes forming a pair of hollow insulating members 22 (only one beingshown in FIG. 2), wherein each hollow member includes a cylindrical sidewall 24 extending between a pair of opposed open ends 26. Each hollowmember 22 is fabricated of a high temperature resistant electricallyinsulating material such as glass or ceramic. Alumina is the preferredmaterial for members 22. Each hollow member 22 is formed with an outerdiameter substantially equal to the inner diameter of .side' wall 12 ofhousing 10, and a length slightly less thanthe distance between each endof housing and the closest shoulder 19a or 19b of annular boss 18 tosuch end within the housing. In this manner, each hollow member 22 maybe fitted in the housing with one end 26 of said member in contact witha shoulder 19a or 19b and the other end of said member lying near oneend of the housing. This relationship is more completely describedbelow.

Preferably, although not essential to the method of this invention, eachhollow member 22 is formed with at least one circumferential groove 28in side wall 24.

I then snapped into a particular groove 28.

Referring now to FIG. 4, and in accordance with the next step of themethod of this invention, a pair of electrode rods 32 are formed toserve as the two line connected electrodes of the arrestor. Thus, rods32 are fabricated of an electrically conductive material such as metal,preferably copper. Preferably, each rod is comprised of a solidcylindrical shaft 33 extending between opposing ends 38 and 39 thereof,and including a stop or flange 34 formed thereon. As shall be describedin more detail below, stop 34 cooperates with a welding flange 20 onhousing 10 to guide the rod into concentricity with the housing.

Preferably, stop 34 comprises a circular base portion 36 and an inwardlytapered or frusto-conical shoulder 37. More specifically, shoulder 37 istapered from a maximum diameter at base portion 36 which is less thanthe diameter of base portion 36, to thereby define an annular rim 39 atthe outer periphery of the shoulder. Shoulder 37 tapers to a minimumdiameter adjacent shaft 33 which is greater than the diameter of shaft33. It is important that the line of intersection of shoulder 37 withbase portion 36 be equal in diameter to the inner diameter of eachwelding flange 20 at outer edge 23 thereof.

With such arrangement, it will be noted that when end 38 of electrodeshaft 33 is inserted into housing 10, such as through end 16 thereof,and in the event the electrode shaft is initially eccentric with thehousing, a portion of welding flange 20 at housing end 16 will engagefrusto-conical shoulder 37 to thereby direct the shaft laterally intoconcentric alignment with the flange edge 23 and thus with the housing,which concentricity isestablished when edge 23 of the welding flangeengages base portion 36 of stop 34. Further, with edge 23 of the weldingflange at the line intersection between base portion 36 and shoulder 37,the electrode rod will be restrained from further movement laterally ofits axis thereby being maintained in concentric alignment with thehousing.

Continuing with the description of the method of this invention, afterhousing 10, hollow members 22, and electrodes 32 have been formed,solder rings 30 are snapped into associated grooves 26 in hollow members22. Then, each hollow member is inserted into housing 10 through adistinct end thereof in the manner above described. This is followed byinserting one electrode rod 32 through the associated hollow member 22into the interior of housing 10, the inward progression of saidelectrode being guided into concentricity with the housing by thecooperation of welding flange 20 with stop 34 in the manner abovedescribed.

Referring now to FIGS. 6 and 6A, the nextstep of the method of thisinvention comprises securing the one electrode to an associated end ofthe housing. This is preferably accomplished by heating such end of thehousing to weld the electrode thereto. In such welding process, the rodis preferably moved further into housing 10 by applying an inward forcethereto so that the welding flange will melt down and effect a hermeticseal between the flange 36 and the housing 10. This is preferablyaccomplished by resistance welding, although other well known weldingtechniques may be employed.

The solder ring 30 closest the end of the electrode which has beenwelded to the housing is softened to seal the housing to the adjacenthollow member 22. It will be realized that if the application ofexternal heat is used to weld the electrode to housing 10, the solderring 30 in the hollow member 22 adjacent the flange 36 will be caused tomelt thereby simultaneously effecting a hermetic seal between thehousing side wall and such hollow member.

After one electrode 32 has been welded to end 16 of housing 10, theother electrode 32 is disposed concentrically within the housing and allof the air in the interior of the housing is evacuated therefrom byaconventional vacuum assembly (not shown). (It will be recognized thatthe second electrode could have been so positioned earlier in theprocess and then held in its concentric position by suitable means.) Atsome point in the process up to this point, preferably at this point,the two inner solder rings 30 are softened to form second hermetic sealsbetween hollow members 22 and metal wall 10. The purpose of this willbecome apparent hereinafter. The housing is then preferably transferredto a conventional dry box'which typically contains dry nitrogen. At thispoint, a noble gas, such as argon, is injected into the dry box to driveout the nitrogen whereupon the noble gas passes into the interior ofhousing through non-welded end 14 thereof. Then, the nonwelded electrode32 is secured to end 14, preferably in accordance with the procedureabove outlined for welding the first electrode to end 16 of housing 10.The assembled structure is shown in FIG. 6 wherein the pair ofelectrodes represent the two active terminals of a three-terminalvoltage surge arrestor.

So structured, it will be noted that an interelectrode gap 40 is formedbetween the inner ends 38 of the pair of electrode rods, and that thegap 41 is formed between the electrode rods and boss 18 of housing sidewall 12. Preferably, the extent of gap 40 in a direction parallelto axis21 of the housing substantially equals the extent of gap 41 in adirection perpendicular to said axis. It has been found that suchrelationship between gap 40 and gap 41 optimizes the efficiency of thearrestor and, in fact, is a requirement of a true threeterminal voltagesurge arrestor.

Referring now to FIG. 7, the next step in the method of this inventionwill be described. More specifically, it is desired that the side wall12 of housing 10 contain a segment 42 thereof to be grounded and used asthe third and ground terminal of the surge arrestor. To this end, it isimportant that at'least a portion of such a segment include boss 18 sothat when the gas is ionized, the current flow will be from theelectrodes through gap 41 to ground.

In forming segment 42 of housing side wall 12, it is essential 'toisolate the segment from the pair of electrode rods 32. One way ofaccomplishing this is to remove a complete circumferential portion ofhousing side wall 12 near each end of the housing leaving segment 42(FIG. 7) between the spaces formed in the housing side wall with saidportions removed. Preferably, each such portion is removed from thehousing side wall in an area between the pair of solder rings in eachhollow member 22. For example, see spaces 44 and 46 formed in housingside wall 12 thereby defining segment 42 therebetween (FIG. 7). Apreferred way of removing the pair of housing portions to form spaces 44and 46 is by placing housing 10 on a lathe or the like and carving outannular rings between each of the two pairs of solder rings in thehollow members. Then, segment 42 is isolated from electrodes 32 and mayserve as the third or ground electrode.

In accordance with the method as above outlined, a three-terminalvoltage surge arrestor 50 is formed, as shown in FIG. 7. The operatingcharacteristics of surge arrestor 50 will be defined by the nature andcharacteristics of the specific gas and electrically conductivematerials used, as well as by the dimensions of gaps 40 and 41.

Although the above invention has been described with reference to aspecifically disclosed embodiment, the invention is not to be solimited. Rather, the invention is deemed to include obviousmodifications and alternations to the specific embodiment abovedescribed.

Other obvious modifications and alternations within the skill of theartworker are contemplated in this invention. The precise scope of thisinvention is to be defined in the following claims.

What is claimed is:

1. A method for fabricating a three-terminal voltage surge arrestorcomprising the steps of:

a. forming an electrically conductive hollow housing having acylindrical side wall extending between opposed open ends of thehousing, the side wall including a welding flange at each end of thehousing extending outwardly in a direction substantially parallel to thelongitudinal axis of the housing;

b. forming a pair of electrically insulative hollow cylindrical membersfor receipt within the housing adjacent opposing ends thereof;

c. forming a pair of electrode rods each including means thereon forengaging the welding flange at an end of the housing as the rod isinserted into the housing through such end thereof to concentricize therod in the housing;

(I. positioning the pair of hollow members in the. housing adjacentopposing ends said housing and securing said hollow members in sealedrelation to said housing;

e. inserting the electrode rods into the housing through said hollowmembers until said means on each rod engages an associated weldingflange on the housing side wall to concentricize the rod in the housing;

f..securing in sealed relation therewith one electrod rod to an end ofthe housing;

' g. withdrawing air from the interior of the housing through the otherend of the housing;

h. injecting a readily ionizable gas into the interior of the housingthrough said other end of the housing;

i. securing the other electrode rod to the other end of the housing; and

j. electrically isolating a central segment of the housing side wallfrom both electrode rods.

2. The method of claim 1, wherein the means for engaging the weldingflange to concentricize said rods comprises a base on each said rodextending radially outward therefrom and a frusto-conical shoulderaxially aligned with said rod and base and having a maximum radiusadjacent said base and slightly smaller than the diameter of saidwelding flange, whereby axial movement of said electrode rods inward ofsaid housing will laterally shift said rods when they are originallyeccentric of said housing in a direction to concentricize said rods. r

3. The method of claim 2, wherein the step of forming the pair of hollowmembers includes forming a pair of spaced apart circumferential groovesin the side wall of each hollow member, and wherein the hollow memb.positioning each solder piece in a groove in the side wall of aparticular hollow member, which solder piece will melt upon theapplication of heat to effect a pair of spaced apart hermetic sealsbetween said particular hollow member and the housing.

4. The method of claim 3, wherein the isolating step includes removing acomplete circumferential portion of the housing side wall between eachpair of hermetic seals.

1. A method for fabricating a three-terminal voltage surge arrestorcomprising the steps of: a. forming an electrically conductive hollowhousing having a cylindrical side wall extending between opposed openends of the housing, the side wall including a welding flange at eachend of the housing extending outwardly in a direction substantiallyparallel to the longitudinal axis of the housing; b. forming a pair ofelectrically insulative hollow cylindrical members for receipt withinthe housing adjacent opposing ends thereof; c. forming a pair ofelectrode rods each including means thereon for engaging the weldingflange at an end of the housing as the rod is inserted into the housingthrough such end thereof to concentricize the rod in the housing; d.positioning the pair of hollow members in the housinG adjacent opposingends said housing and securing said hollow members in sealed relation tosaid housing; e. inserting the electrode rods into the housing throughsaid hollow members until said means on each rod engages an associatedwelding flange on the housing side wall to concentricize the rod in thehousing; f. securing in sealed relation therewith one electrode rod toan end of the housing; g. withdrawing air from the interior of thehousing through the other end of the housing; h. injecting a readilyionizable gas into the interior of the housing through said other end ofthe housing; i. securing the other electrode rod to the other end of thehousing; and j. electrically isolating a central segment of the housingside wall from both electrode rods.
 2. The method of claim 1, whereinthe means for engaging the welding flange to concentricize said rodscomprises a base on each said rod extending radially outward therefromand a frusto-conical shoulder axially aligned with said rod and base andhaving a maximum radius adjacent said base and slightly smaller than thediameter of said welding flange, whereby axial movement of saidelectrode rods inward of said housing will laterally shift said rodswhen they are originally eccentric of said housing in a direction toconcentricize said rods.
 3. The method of claim 2, wherein the step offorming the pair of hollow members includes forming a pair of spacedapart circumferential grooves in the side wall of each hollow member,and wherein the hollow members are secured in sealed relation to saidhousing by: a. forming a piece of solder for each groove of a size andshape enabling such piece to be positioned within the groove alongsubstantially the entire circumferential extent of said groove; and b.positioning each solder piece in a groove in the side wall of aparticular hollow member, which solder piece will melt upon theapplication of heat to effect a pair of spaced apart hermetic sealsbetween said particular hollow member and the housing.
 4. The method ofclaim 3, wherein the isolating step includes removing a completecircumferential portion of the housing side wall between each pair ofhermetic seals.